<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // 声明
        let age
        // 赋值
        age = 30
        // 声明并赋值
        let name = 'tom'
        document.write(age)
        document.write(name)
    </script>
</body>
</html>